Because of their wide availability, relative inexpense and versatility, polyurethane elastomers with specific physical properties have been adapted for use in a diverse array of technical applications. One such application is as conductive and semi-conductive members in image forming devices. It has been desirable to develop more compact image forming devices having a smaller device footprint. Consequently, the need for development of reduced-geometry printer components arose. However, it has been discovered that the necessary size adaptations alters the functioning of various elastomeric components with respect to, for example, required compressive forces, nip widths, low compression set, low hardness, triboelectric charging capacity, and rotational torque. Utilization of reduced-geometry components having the same elastomeric properties as the originally-sized components often result in the occurrence of unacceptable print variations and distortions in the final printed product. Hence, new materials adapted to confer physical properties which would compensate for the reduced-geometry and restore the quality of the final printed product are needed.
In particular, polyurethane elastomers have been used as roll components of a laser printer. Generally, a polyurethane elastomer is formed by sufficiently curing a polyurethane mixture typically comprising a prepolymer to provide the polymer backbone, and one or more curatives (typically chain-extenders and/or cross-linkers), as well as various solvents, catalysts, and other additives depending on the need. Typically, curatives comprise at least di-functionality, to act as chain extenders or tri-functionality to act as cross-linkers to promote networking within the matrix, functional groups being generally defined as groups comprising active hydrogens, for example, amines or hydroxyls.
Reaching a desired elastomer hardness by manipulating selection of the urethane prepolymer and monomers forming the curative components of the final elastomer often results in unacceptable compromises in other properties of the elastomer. Typically, plasticizers are used to reduce the hardness of polymeric elastomers such as cast urethanes. However, plasticizing additives, which are not chemically bonded into the polymer matrix, and are therefore free to migrate throughout the roll, including to the surface, may cause problems in electrophotographic print applications. At the surface of the developer roll, these migrating additives interact with the toner particles, causing the toner particles to undesirably coalesce.
Hence, there is a clear need for softer polyurethane elastomers having low hardness and for methods of manufacturing them. In addition, it would be advantageous to provide inexpensive, more versatile curatives, which could confer desirable property profiles to polyurethane elastomers required by particular applications.